1. Field of the Invention
The present invention relates to a method of chemically recycling waste polyethylene terephthalate such as polyethylene terephthalate (hereinafter referred to as PET) bottles. More particularly, the present invention relates to a polymerizable unsaturated resin composition which contains a polyester skeleton derived from polyethylene terephthalate as a resin skeleton of a radical polymerizable resin and also has an excellent low-temperature curing property, and maintains practical physical properties such as elongation, toughness, flexibility, and strength, wherein PET, which is capable of curing completely even in the presence of air, is used as an essential raw component in an effective method utilizing collected PET.
2. Description of Related Art
(Meth)acryloyl group-containing polyester resin compositions comprising a straight-chain polyester having a (meth)acryloyl group at both ends of molecules and an ethylenically unsaturated monomer are known as disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 03-002212 and Japanese Unexamined Patent Application, First Publication No. Hei 04-202410.
Unsaturated polyester resin compositions comprising an unsaturated polyester and an ethylenically unsaturated monomer, wherein PET is used as a raw material, are also known as disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 08-151438 and Japanese Unexamined Patent Application, First Publication No. Hei 08-295729.
However, none of these resin compositions of the prior art were produced by effective utilization of waste PET, but they were produced using a conventional industrial raw material.
An object of the present invention is to provide a practical polymerizable unsaturated polyester resin composition, wherein a polyester skeleton derived from collected PET is introduced, for effective utilization of waste PET such as a PET bottle which has recently been considered a large obstacle to environmental protection.
Another object of the present invention is to provide a polymerizable unsaturated polyester resin composition having excellent elongation, toughness, flexibility, and strength by using collected PET as an essential raw component.
To solve the problems described above, the present inventors have made intensive studies into the development of a polymerizable unsaturated polyester resin obtained by using collected PET as an essential raw component, thus completing the present invention.
Namely, the present invention provides a polymerizable unsaturated polyester resin composition comprising a straight-chain polyester (A) having a (meth)acryloyl group at both ends of molecules and an ethylenically unsaturated monomer (B), said straight-chain polyester (A) having a (meth)acryloyl group at both ends of molecules being obtained by reacting (a) a terephthalate oligomer having a hydroxyl group at both ends of molecules resulted from the alcoholysis reaction of collected waste polyethylene terephthalate by an aliphatic glycol having an ether bond, (b) a dibasic acid containing an aromatic dibasic acid as a principal component and (c) a glycidyl (meth)acrylate.
The resin composition of the present invention is particularly excellent for use as a resin for coating material because of its excellent performances such as elongation, toughness, flexibility, low-temperature curing property, strength, air-drying property, and low shrinkage property. The present invention provides a chemical recycling method and an effective utilization method as a method of treating waste PET bottles, which has recently been considered as a large problem in view of environmental protection.